Thanks for your help. It righted itself with no action on my part. Go figure!

And I do have an internet connection on my PC - most of the time. NZ broadband is a bit unreliable and so when it goes offline, I like to be able to use my mobile to connect so I don't have to stop working.

Thanks for the help but it all seems quite complicated when it was 'plug and play' originally and just stopped working for no reason. Mind you, my PC started shutting down every night and when I investigated, the Windows update setting had been changed to automatic, instead of letting me decide to install. How??? I hadn't touched it! Chances are an update has screwed something up.

You definitely can, because I was doing it up until today! Like with my old iPhone 3GS, I just plugged it in and it was available in the Network and Sharing Center. However, whereas the iPhone automatically became a hotspot when tethered, with the S3 each time you go to settings and switch on the 'Tethering and portable hotspot' & it warns you that the Wifi will then be turned off. It's only today that it needed a password. I can't see any settings in 'Tethering and portable hotspot' apart from the slider to switch it on, USB or Bluetooth tethering and Help (which isn't).